Prior art optical design within optical imaging systems has primarily focused on optical elements and the detector used to capture an image. Such optical elements typically include lenses and mirrors that focus and magnify optical radiation. The detector is, for example, an analog detector (e.g. film) or a digital detector (e.g., CCD or CMOS array) that detects the optical radiation to render a final image.
Mechanical adjustment of optical elements is also known in the prior art to control and obtain best focus within optical imaging systems. The most common method of mechanical adjustment is to vary the distance of the image plane by moving a lens. Other mechanical adjustment methods involve interchanging lens elements with different focusing power.
One form of optical focusing through mechanical means involves transverse movement of two optical elements, as described in U.S. Pat. No. 3,305,294. In the '294 patent, a pair of aspherical optical elements moves transversely in equal but opposite displacements. The form of the aspherical optical elements is defined by polynomials that are strongly dependent on the cubic terms of a power series of two variables.
An improvement to the focusing method in the '294 patent is described in U.S. Pat. No. 3,583,790. The '790 patent allows lateral movement of only one aspheric optical element as opposed to two aspheric optical elements, as required by the '294 patent.
Another method of modifying focus is described in U.S. Pat. No. 4,650,292. In the method of the '292 patent, two or more aspherical optical elements are rotated about axes decentered with respect to the optical axis, to modify focus.
The aforementioned prior art thus facilitates obtaining best focus within the imaging system by using mechanical means. If one of the optical elements of the imaging system changes, e.g., due to thermal conditions, then the system may lose focus and, unacceptably, the image. Moreover, aside from changes in focal length and aperture, the depth of focus, depth of field and amount of anti-aliasing of the imaging system remain unchanged. Furthermore, if there is a change of focal length and/or aperture, there is no present way, for example, to maintain a fixed depth of focus, depth of field and/or anti-aliasing effects, if desired.
The aforementioned patents (U.S. Pat. Nos. 3,305,294; 3,583,790; 4,650,292) are incorporated herein by reference.